1. Field of the Invention
This invention relates to a method of exposing a peripheral part of wafer which is used for a fine pattern formation process in the processing of ICs, LSIs or other electronics elements. More particularly, this invention relates to remove, in a development step, an unnecessary portion of a photoresist coated on a semiconductor substrate, typically a silicon wafer, or a substrate consisting of a dielectric, a metal or an insulator.
2. Description of the Prior Art
In the manufacture of ICs and LSIs, for forming a fine circuit pattern of a photoresist pattern is formed by coating a photoresist on the surface of a silicon wafer or the like and exposing and developing the coated photoresist. The photoresist pattern thus formed is used as a mask to effect ion implantation, etching, lifting-off and other steps.
Usually, the photoresist is coated by spin coating. The spin coating process is disclosed in Japanese Un-examined Patent Publication("KOKAI KOHO" in Japan) 61-79227 and 61-73330. In the spin coating process, the wafer is spun while pouring photoresist onto the center position of the right side of the wafer and the poured photoresist is coated on the right side of the wafer by centrifugal forces. In this spin coating process, however, the photoresist gets off the peripheral part of the wafer and is brought to the wrong side of the wafer.
The photoresist, which is coated on the peripheral part of wafer and brought to the wrong side of the part, is not exposed in a exposing process for forming circuit pattern. Therefore, these photoresists remain unnecessary after development.
The remaining unnecessary photoresist coated on a peripheral part of wafer gives rise to the following problem. The wafer with the photoresist coated is conveyed in various steps and by various systems or units. A peripheral part of wafer thus is sometimes mechanically chucked and sometimes rubs walls of wafer cassette or like wafer accommodation means. In such cases, the unnecessary photoresist portion on the peripheral part of wafer is liable to be removed and re-attached to the pattern formation part of the wafer. In this case, correct pattern formation can no longer be obtained, thus reducing the yield.
The fact that the unnecessary photoresist remaining on a peripheral part of wafer becomes "refuse" to reduce the yield poses significant problems particularly in view of the recent trend for higher functional level and finer pattern in Integrated Circuit. So, for removing the unnecessary photoresist remaining on a peripheral part of wafer, a technique of removing the photoresist by a solvent spray method is in practical use.
In this method, the solvent is sprayed on the wrong side of a peripheral part of wafer, solving and removing the unnecessary photoresist.